Phosphorous-based ligands are useful as part of the catalyst system in industrially important reactions such as hydroformylation and hydrocyanation. The useful ligands include phosphines, phosphinites, phosphonites, and phosphites. See PCT patent applications WO 99/06146 and WO 99/62855. Both mono(phosphorous) ligands and bis(phosphorous) ligands are utilized in the art. Mono(phosphorous) ligands are compounds that contain a single phosphorus atom which serves as a donor to a transition metal, while bis(phosphorus) ligands, in general, contain two phosphorus donor atoms and typically form cyclic chelate structures with transition metals.
Processes for the preparation of 3,3′-dialkyl-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-binaphthols, unlike their 3-alkyl-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-binaphthol analogs, appear in the literature. One such process, disclosed in J. Chem. Soc., C 1971, 23, teaches the preparation of 3,3′-di-t-butyl-5,5′,6,6′,7,7′8,8′-octahydro-2,2′-binaphthols by the coupling of 3-t-butyl-5,6,7,8-tetrahydro-2-naphthol using potassium ferricyanide and FeCl3-based methods with yields of only 25% and 6%, respectively. Also disclosed is the coupling of 3-t-butyl-5,6,7,8-tetrahydro-2-naphthol to give 3,3′-di-t-butyl-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-binaphthol can be carried out with a large excess MnO2 (20 times in weight).
Another process, disclosed in Acta Chem. Scand. 1970, 24, 580, teaches the coupling of 3,4-dimethyl-5,6,7,8-tetrahydro-2-naphthol to give 3,3′,4,4′-tetramethyl-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-binaphthol with 43% yield. J. Org. Chem. 1978, 43, 1930 discloses the preparation of 3,3′-dimethyl-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-binaphthol by LiAlH4 reduction of 3,3′-di(bromomethyl)-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-binaphthol.
There has been no report in the prior art regarding acid catalyzed alkylation of 5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-binaphthol to produce 3-alkyl-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-binaphthols or 3,3′-dialkyl-5,5′,6,6′,7,7′8,8′-octahydro-2,2′-binaphthols. Acid catalyzed alkylation of phenols is known. For example, U.S. Pat. No. 4,912,264 discloses heteropoly acid catalyzed phenol and naphthol alkylation. U.S. Pat. No. 2,733,274 discloses cresol sulfonic acid catalyzed phenol alkylation. J. Am. Chem. Soc., 1945, 67, 303 discloses aluminum chloride catalyzed phenol alkylation. Industrial and Engineering Chem., 1943, 35, 264 discloses sulfuric acid catalyzed phenol alkylation. Friedel-Crafts alkylation of aromatic compounds has also been reviewed. For example, see Olah, G. A. Friedel-Crafts and Related Reactions, Wiley-Interscience: New York, 1964, Vol. II, part I, Roberts, R. Friedel-Crafts Alkylation Chemistry, Marcel Dekker, 1984, and March, J. Advanced Organic Chemistry, 4th Edition, Wiley-Interscience: New York, 1992, pp 534–539.
Recently, it was disclosed that rare earth metal trifluoromethanesulfonates as water-tolerant Lewis acid catalysts can be utilized in Friedel-Crafts alkylation of benzene and phenol derivatives with secondary alkyl methanesulfonates. See SynLett, 1998, 255–256 and Synthesis, 1999, 603–606.
It is not practical to use LiAlH4, a large excess of MnO2, or even a stoichiometric amount of potassium ferricyanide to carry out industrial scale preparations of alkylated, hydrogenated binaphthols. Such a process would be expected to generate a large amount of byproducts. Therefore, a need exists in the art for a practical and general method to prepare 3-alkylated-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-binaphthols and 3,3′-dialkylated-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-binaphthols.